This invention relates to a method of assembling electrolytic cells and particularly to a method for assembling membrane-type electrolytic cells.
Electrolytic cells have been developed which are based on the design principles used in the unit operation of "filter presses" used to filter solids from liquids. These "filter press" cells have followed the practice originated with filter presses of assembling plates or frames housing electrodes with intermediate membranes into a "bank" of frames supported with the frames in a vertical plane on a filter press skeleton structure. In general, this is a convenient method of assembling since the frames may be stored in place and may be shifted back and forth as the cell is assembled or dismantled. In the filtration field, presses are commercially available that shift frames automatically according to a program. Such presses are generally used with filter press electrolytic cells in order to simplify repairs by providing easier access to individual membranes and electrodes in the cell bank. This technique of using a long cell bank and a shifting press has several disadvantages. In particular, it is difficult to hold a membrane which may be wet, slippery, heavy, fragile and soaked with caustic soda, while trying to simultaneously hold the electrode frames in a spaced position to provide enough space between the electrode for fitting the membrane between the two spaced vertical frames and between any cross-frames or other device used to space the frames to obtain a satisfactory seal or fit. The membranes, which are very expensive compared to conventional diaphragms, may tear or "bag" out of shape or even fail to seal on all gasket surfaces. Furthermore, it is extremely awkward and difficult to manipulate large, high electrode frames in such a filter press apparatus and, therefore, the height of the cell is limited by practical considerations in order to allow operators to observe and repair minor gasket or membrane irregularities on many parts of the frame circumference, e.g. top, bottom, and high sides. Although such a height limitation has been conventionally imposed upon filter press cell designs, it would be desirable and advantageous, if possible, to develop a much higher cell in order to increase the amount of product which can be produced using a given amount of floor space in the plant in which the cell is contained.
It has also been found that treating or conditioning the membranes is essential if the electrolytic cell is to operate at optimal efficiency after assembly. Generally, the membranes are received in a nonionic state and must be converted to an ionic conductive form. Additionally, failure to treat or condition the membrane prior to cell assembly will cause excessive swelling or shrinkage of the membrane after the membranes are emplaced within the cell and operation of the cell begun. Excessive swelling causes wrinkling in the membrane after cell assembly. This wrinkling creates a crease that generally bears against the anode and is attacked by chlorine. Apparently the crease from the wrinkle becomes hardened and splits along its top. Alternately, where excessive shrinkage occurs, cracking or rupturing in the membrane will occur. Either of these two situations where there is a physical break in the surface of the membrane causes the cell to dramatically drop in operating efficiency because the caustic solution within the anode is permitted to flow into the anolyte. The quantity of chlorine gas produced also decreases while current consumption dramatically increases. Additionally, chlorate levels increase in the anolyte and catholyte fluids.
A solution to these and other problems is achieved with the present invention by providing a method of assembling a monopolar filter press-type electrolytic cell by treating or conditioning the membranes, assembling a vertical stack or horizontal electrode frames with a horizontal membrane sheet between each pair of opposed frames, applying pressure to the opposite vertical ends of said stack to vertically compress the stack, rotating the compressed vertical stack from a vertical orientation through approximately 90.degree. and connecting and operating the assembled cell in an electrolytic circuit.